Open clusters are known to be the birthplace of most field stars. As such they can be treat- ed as benchmark for studies of stellar and Galactic evolution. Because of its unusually advanced age (3-4 Gyr), its proximity to the Sun (800-900 pc), and its Sun-like chemical composition, M67 has become one of the most extensively studied open clusters in the Milky Way. Many of M67's sub-giant branch, giant branch, and red clump stars were spectrometered in the APOGEE survey. Combining proper motions, radial velocities, colour-magnitude properties, and metallicities, we carried out a careful membership anal- ysis of the stars observed within the projected diameter of M67. We then investigated the abundances of several elements in cluster member stars as measured by the APOGEE pipeline ASPCAP. Along the sub-giant and giant branch we detected effects of the first dredge-up, as the products of the CNO cycle in the hydrogen-burning shell are brought to the surface by convection in the envelope, thus changing the surface abundance of [C/Fe] and [N/Fe]. We compared the abundances of these elements with the stellar evolution models by Salaris et al. (2015), which we find to be in very good agreement with the mea- sured [C/N] abundances of the M67 red giants, thus posing a strong constraint on the calibration of [C/N] as an age indicator for field stars.